Detection and distribution of haematophagous flies and lice on cattle farms and potential role in the transmission of Theileria orientalis

Abstract

On the Northern Tablelands of New South Wales, Australia, endemic <i>Theileria orientalis</i> infection of cattle has been reported on farms where no ticks have been observed, raising the question of how <i>Theileria</i> is transmitted in these areas. To investigate the potential role of mechanical transmission by insects, the present study investigated the seasonal dynamics of biting fly species trapped between December 2017 and May 2019 on six cattle farms in the region where the presence of <i>Theileria</i> was confirmed. These flies, sucking lice collected from these farms and pools of <i>Culicoides</i> species affecting cattle also trapped in the region were subjected to qPCR detection of <i>T. orientalis</i>. Eleven species from eight genera of biting flies were collected using unbaited Nzi traps. Tabanid species were present in all farms, with <i>Dasybasis oculata</i> (43.6 %) and <i>D. circumdata</i> (27.6 %) being the most abundant and widespread species. The effect of season on the mean count per trapping event was statistically significant and highest in the summer months for <i>Lilaea fuliginosa</i> and <i>D. oculata</i>, and the autumn months for <i>D. circumdata</i>, with no seasonal effect on the abundance of the undescribed <i>Dasybasis spp.</i> No biting flies were trapped during the winter months. Sucking (<i>Linognathus vituli</i> and <i>Haematopinus eurysternus</i>) and biting (<i>Bovicola bovis</i>) cattle lice were also collected from all farms with the latter detected in only one farm. PCR screening for <i>T. orientalis</i> of trapped hematophagous insects resulted in parasite detection in the tabanid and Stomoxyini flies, biting midges and sucking lice with the highest proportion of positive samples for <i>Haematopinus eurysternus</i> (4/4 pools) and <i>H. irritans exigua</i> (6/15 individuals). The detection of the parasite in these potential vectors indicates a possible role in the mechanical transmission of <i>T. orientalis</i> and may partly explain the ubiquitous presence of <i>Theileria</i> in areas where ticks are absent.